1. Field of the Invention
This present invention relates to motor vehicles.
2. Description of the Prior Art
Aerodynamic efficiency is a high priority in design of air vehicles. In design of automobiles it ranks below a list of requirement that conflict with efficiency, some of which are rarely questioned. Such are requirements for two front seats, ease of implementation, and fashion conformity. When energy is inexpensive and inexhaustible, such requirements are not a problem. Technological innovations, for example electric drive systems capable of regenerative braking, are interesting curiosities. Adequate motivation for significant innovation is lacking and key decision makers need have no understanding of innovative possibilities. Thus, when the energy equation is significantly changed, the world wide motor vehicle industry is ill equipped to adapt effectively. In such a world, minor improvements pass for important progress. Useful principles, if not completely forgotten, are poorly understood.
A basic concept in aerodynamics is that of drag coefficient. At any given speed the actual drag force is proportional to the product of projected frontal area and the drag coefficient value. While the drag coefficient value is a function of Reynolds number, for vehicle sizes and speeds of interest that drag coefficient value is reasonably constant. An effort to reduce the width of cars by eliminating the right front seat, as in U.S. Pat. No. 7,338,061, Bullis, Mar. 4, 2008, accomplished a significant reduction in projected frontal area. Further aerodynamic drag force reduction depends on reduction of drag coefficient.
The ideal airship shape is available from the history of aerodynamic research. Prior to developing the modern airplane wing shape, Prandtl and his students at his Gottingen University laboratory in Germany, with cooperating American researchers, studied the aerodynamics of airships. Such vehicles were of great interest in 1906, their use continuing through WWII. A typical airship shape was developed that was roughly a cylinder with tapered ends, this being a body of revolution about an axis aligned with the flight direction. Prandtl showed that drag force due to accelerative effects could be almost eliminated by a refined taper function. Only a small viscous drag then remains. Wind tunnel test results are available that can be scaled to dimensions appropriate for the automobile. In spite of this background, very little of this technology has been used in the design of road vehicle.
It appears that a large impediment to progress in this regard is the nearly universal requirement for seating arrangements that include, at least, two front seats. Therefore, to enclose two adults seated in such front seats in a body of revolution requires that such a body be about six feet in diameter. Thus, the attempt in the 1930 era to utilize the airship resulted in a car known as the Dymaxion. This example is said to have achieved improved gas mileage for its day, but nothing like what might be expected for a body of revolution somewhat similar to the ideal airship known to Prandtl. A significant difference was that it was not significantly elevated above the ground. Given that stability of this vehicle was a concern, that limitation seems inescapable.
The kind of thinking ingrained in the process of automobile design is illustrated in a Mercedes Benz press release that discusses development of an automobile based on a nearly ideal aerodynamic body form. They utilized the shape of an unusual looking fish known as the box-fish known for low hydrodynamic drag. The initial test model was shaped like that fish and wind tunnel tests showed it to be subject to extremely low air drag. It is not noted in the release, but having width approximately equal to height means that this functions much like a body of revolution. They do discuss the effect of testing at a significant separation distance from the ground, such that free flow aerodynamic conditions are maintained. While they measured extremely low drag in free flow conditions, when more realistic conditions were represented, by testing in proximity to the ground, they suffered a 50% penalty in drag coefficient. They further indicate that adding other features necessary for a realistic car, as well as the provision for operation close to the ground, causes a degradation of drag resistance of more than 200% relative to the ideal body test results in free flow conditions. Such features included wheel wells that provide for wheel steering and suspension devices. The inability of these experts to achieve better results can be attributed to their ground rule, as stated by the press release, that the vehicle width required for seating two persons was six feet. Apparently, a single wide car is inconceivable, at least for major production auto makers. Thus, they are barred from realization of the accumulating advantages of such an arrangement, where a reduction in projected frontal area, closer adherence to the ideal shape, and practicality of elevating such a shape are realizable measures to improve efficiency. The wide form naturally leads to a flat bottomed form which further exacerbates the degradation in drag coefficient caused by proximity to the ground. While this development effort achieved a significant improvement in aerodynamic efficiency, it came far short of the level of performance originally suggested by the box-fish ideal shape. This development process thus illustrates the requirements and assumptions that are a basic part of the present day automotive design process.
A practical rule for achieving an approximation of free flow conditions can be postulated based on a ground separation requirement related to the frontal projected area, where this rule stipulates an elevation sufficient for achieving a significant practical performance advantage. For bodies of revolution and for rectangular shapes having width greater than height, an approximate elevation standard is one half of the square root of the projected frontal area. Applying this rule to a six foot wide body of revolution car, where two people can ride side-by-side, leads to an overall car height of over eight feet. This would obviously not appeal to car designers.
It might be supposed that a narrow car would have been considered by the Mercedes-Benz project team that worked on the box fish shape, were a practical way to stabilize such a car available. The previous invention that might have been useful in this concept work, U.S. Pat. No. 7,338,061, Bullis, Mar. 4, 2008, was not available at that time.
Faced with these realities, the nearly universal choice has been to give up on the ideal body form and any attempt at elevation. In fact, most designs go in the opposite direction. Efforts to make cars economical usually result in a very low vehicle body height that is spaced as close as possible to the ground. The designs usually direct air flow over, and to the sides of, the car. At least this ends up with low and wide car that is naturally stable. The obvious drawback of significantly uncomfortable seating and unpleasant height of eye has never been widely accepted by car buyers. The automotive industry has, thus, failed to show a development path capable of addressing present fuel efficiency concerns.
An exception is suggested by a developmental vehicle called the Aptera, which appears to the published description to be a very lightweight vehicle, probably less than a large motorcycle; with an extremely wide wheel base, apparently about as wide as that of a large truck. This is reported to be an aerodynamic shape designed by an optimizing, finite element computer code, where the coefficient of drag seems to be nearly ideal. Inspection of the published information seems to show a ground clearance that allows some increase of air flow under the vehicle, compared to typical cars. This ground clearance, together with the body shape, appears to be working to minimize ground surface effect, whether or not this was an intention of the designers or a determination made by the optimizing computer code. The vehicle is still very low overall, and this appears to be at the expense of rider comfort, where two adults are said to be riding side by side, with very little headroom. Since there is no provision for stabilization beyond weight in the vehicle body and the wide wheel base, it is important that the overall height be as low as possible. Given that it carries two adults side by side, this vehicle is a remarkable achievement in aerodynamic design. It shows the potential for shape refinement of the finite element method.
There have been some attempts to produce a narrow car with seating width for only one person. The Stanley Steamer race car of 1885 was for a single person and it was built with some meaningful consideration of aerodynamic performance. However, its open cockpit and exposed driver prevented most of the intended low drag effect. The cycle cars of the 1910 era were also narrow, but aerodynamic shape was not a significant part of these designs. Cars were produced in the 1950 era with single wide seating, such as the Messerschmitt, which also was very carefully shaped for aerodynamic effect, but this also was very low to the ground. Designing a car with an elevated body on a conventional wheel base would require addition of significant, low placed weight to achieve a stable vehicle. However, gas mileage goals have always tended to encourage car designs that were light weight, especially where the usual propulsion machinery had no capability to recapture kinetic energy by use of regenerative braking. Rolling resistance due to friction in tires and drive train apparatus further discourages heavy vehicles. Consequently, there could be little incentive in the past to create a car having an elevated body.
A high and narrow vehicle, where persons were seated singly or in tandem, was discussed in U.S. Pat. No. 7,338,061, Bullis, Mar. 4, 2008 (hereby incorporated by reference). That invention focused on providing a method of stabilizing such a vehicle using an articulated vehicle arrangement that was a two frame system, having a stabilizer part that was connected to a carriage part with a two axis articulated joint. A streamlined version was also included in this disclosure. A body is said to be streamlined where that body has a controlled contour where stream line convergence is fairly rapid and stream line divergence is very gradual, where a stream line is an imaginary line which is, at the instant of observation, tangent to the velocity vector at every point through which it passes. However, in this arrangement it was necessary for the stabilizer rear wheels to pass under the carriage part and the necessary clearance for this was increased by the need for carriage pitch hinging action. This meant a trade-off had to be made between overall vehicle height and a desire for an uninterrupted aerodynamic carriage surface. It was also necessary for the forward part of the carriage to allow clearance for pitching. This limited shaping possibilities. Further, this disclosure did not provide for an aerodynamic carriage entity that operated independently of the stabilizer part. Neither did it provide for an aerodynamically integrated carriage and stabilizer. Also, this prior disclosure showed the streamlined version as vertically elongated, with its lowest point raised above the ground only high enough to give reasonable clearance of uneven surfaces, with no provision for air flow under the vehicle.
While general vehicle shaping can potentially provide very useful results, failure to attend to details can almost void such benefits. An example of such detail is the wheel well configuration used. In all the years of industry history, only very limited attempts have been made to fix this known cause of automobile and truck inefficiency. Similarly, only sporadic attempts have been made to make the under body surface smooth.
With these limitations, the degree of aerodynamic shaping refinement represented in that prior disclosure was not clearly superior to that of conventional automobiles. Thus the fuel economy improvement was based only on the greatly reduced width. Almost doubling of gas mileage was expected. Although widespread public acceptance of this breakthrough requires rearrangement of the way people sit in cars, this expected improvement in gas mileage is expected to strongly motivate such changes.
However, there remains strong motivation for even further improvement. It is reasonable to expect that the entire world population will increasingly insist on participating in a life style that includes the ability to move about quickly, safely, and comfortably. As life styles are transformed, energy conservation, pollution, and global warming problems will be exacerbated. A major part of the solution to these problems could be a large reduction in the amount of energy needed for transportation. While it is well known that public transportation holds promise in that regard, it is clear that most people prefer distributed living that tends to be inconsistent with practical public transportation systems. It is here assumed that a solution that preserves the fast personal car, with its associated time efficiency and flexibility, will be much more readily accepted.